TemplateStyles (or perhaps more correctly css-sanitizer?) removes spaces between solid and #aaa so that
p { border: 1px solid #aaa; }
is turned into
p { border: 1px solid#aaa; }
It should be noted (for testing purposes) that most modern browsers (Chrome/Firefox/Edge) surprisingly allow this, but IE doesn't.
Minimal test case: https://sv.wikipedia.org/wiki/Anv%C3%A4ndare:Nirmostest/sandl%C3%A5da and https://sv.wikipedia.org/wiki/Anv%C3%A4ndare:Nirmostest/sandl%C3%A5da/styles.css